In mobile communication systems, there is always a challenge to obtain good performance and capacity for a given communications protocol, its parameters and the physical environment in which the mobile communication system is deployed.
Cellular networks are examples of mobile communications systems. Caching concepts are being considered for cellular network for the dual purposes of making more efficient use of network resources and improving the end user service experience (e.g. the “quality of experience”, QoE). Sometimes these two goals can be achieved simultaneously, while other times only one of the aspects may be the target under consideration.
For instance, by a network node (such as a base station) delivering requested content from a network cache instead of from a remote server, network resources may be saved, whilst at the same time reducing the download delay experienced by a user of a wireless device (such as a mobile phone) receiving the requested content.
Another example relates to cooperating caches in the mobile communications system, with one cache in the wireless device (the client) and one in the network, and wherein these two caches cooperate to shift traffic, most notably traffic over the radio interface, from high load periods to low load periods. This is achieved by the network node moving content delivery in time, either by delaying it or by proactively delivering it to the wireless devices in advance. In both cases the network resources required during peak load periods may be reduced, thus allowing a more relaxed peak load dimensioning of network resources. Delaying delivery of data may typically require that the concerned data and application using it are delay tolerant. In terms of user experience, delayed data delivery generally cannot increase the QoE, but if handled properly, it may be performed without decreasing the QoE (or with an acceptable moderate decrease of the QoE). On the other hand, in cases when data can be delivered in advance, traffic load peaks may be reduced whilst simultaneously improving the QoE through reduced delay when the pre-delivered data is actually used by an application in the wireless device. This kind of data delivery (i.e. utilizing low load periods) has been coined “lower than best-effort” service/delivery.
Another aspect of cellular networks relates to reduction of the overall energy consumption of a cellular network. This has the dual purpose of saving the environment and reducing network operation costs. One example of a method for energy consumption reduction could involve enabling network nodes to enter a sleep mode (i.e. a mode of operation wherein as much as possible of the equipment of the network node, e.g. transmitter and/or receiver circuitry, baseband circuitry, etc. is switched off). Hence, during periods of low load a network node may enter the sleep mode, or in other ways switch off (parts of) the equipment controlling one of the network node's cells. The network node may repeatedly enter a wake mode to check for present wireless devices in its coverage area or it may rely on one or more other network nodes/cells to take cover the area while being in the sleep mode. Wakeup signals from other network nodes or from wireless devices have also been considered. Since the energy consumption of the network nodes, in particular base stations, generally represent a large fraction of the overall energy consumption of the cellular network (due to their large number and energy consuming transmissions), this strategy could be an efficient means to reduce the energy consumption. To this end, the concept may be leveraged further to push it to the limits of its energy saving potential, e.g. using features such as micro-sleep (e.g., sleep mode periods on a millisecond time scale or even less) and sleep modes of individual components in the equipment.
With regards to the combination of the caching concept and the network node/cell sleep mode strategy, as described above, one finds that these two concepts may not be readily combined. The caching strategy aiming to move traffic from high to low load periods counteracts the strategy to leverage low load periods to conserve energy by means of a sleep mode. Periods when a network node/cell would ideally enter a sleep mode will, from the point of view of a network based cache, or cooperating network and client caches, appear as excellent opportunities to transfer cached content, either proactive or delayed content transfer. This issue may manifest itself on a millisecond or larger (e.g. seconds, minutes) time scale.
Hence, there is still a need for improved scheduling in mobile communications systems.